The present invention relates to a noncontact type temperature detecting device for use in, for example, copying machines, laser printers and facsimiles. The present invention also relates to a fixing device that employs the temperature detecting device and an image forming apparatus that employs the fixing device.
A conventional noncontact type temperature sensor for detecting the temperature of a fixing roller has comprised a retention part, a resin film mounted to the retention part in such a way that the both surfaces of the resin film are exposed, and a thermosensitive device attached to one surface of the resin film (refer to JP 11-223555 A).
When it is tried to shorten a time required for raising operation of the surface temperature of the fixing roller to a temperature at which the fixing can be achieved (hereinafter referred to as warm-up), it is necessary to improve the response performance of the temperature sensor to the temperature rise of the fixing roller, and to improve the stability performance of the temperature sensor which allows to suppress variations in the detection temperature, which variations are caused by a tolerance in distance to the fixing roller and/or environmental influences.
Improvements in the response performance and the stability performance of the temperature sensor can be achieved by increasing the heat absorption characteristic of the resin film, specifically, by increasing the thermal absorptivity of the resin film, decreasing the thermal emissivity of the resin film and so on.
Accordingly, based on the relation between the film thickness and the thermal absorptivity in the resin film, it can be considered that increase in thickness of the resin film reduces the thermal transmissivity and increases the thermal absorptivity.
On the other hand, however, if the increase in thickness of the resin film increases the thermal capacity of the resin film, which deteriorates the response performance of the temperature sensor.